Packet-Switched Networks

In the mid-1990s, network performance improved to the point
where it became possible to send a stream of media information in real
time across a network connection. Because the media stream is chopped up
into segments, which are then wrapped in an addressing envelope, such
connections are referred to as packet-based. The
challenge, of course, is to send a flood of these packets between two
endpoints, ensuring that the packets arrive in the same order in which
they were sent, in less than 150 milliseconds, with none lost. This is the
essence of Voice over IP.